THE EFFECT OF HYDROGEN CYANAMIDE (DORMEX) ON FLOWERING AND CROPPING OF DIFFERENT APPLE CULTIVARS UNDER TROPICAL CONDITIONS OF SUBOPTIMAL WINTER CHILLING

The effects of pre-bud-break application of 1.5% hydrogen cyanamide (3 % Dormer) on the flowering and cropping of 12 apple cultivars were det ermined over the years 1988/89 to 1991/92 in tropical Zimbabwe, at a s ite with less than 300 h of winter chilling below 7.2 degrees C per ye ar. Control trees, other than those of 'Mutsu' and 'Goldjon' which wer e indistinguishable from the treated trees, showed varying degrees of delayed flowering and low yield in comparison with the cyanamide-treat ed trees. The latter, irrespective of cultivar, attained full bloom wi thin 4-5 weeks of the common date of treatment, so that blossoming of the different cultivars, as well as that of the different trees of eac h cultivar, was synchronized, and all cropped heavily in relation to t ree size. Very satisfactory yields of 'Mollies Delicious', 'Canvada', 'Drakenstein', 'Golden Delicious', 'NJ46', 'Marjorie Pye', 'Spartan', 'Starking', 'Granny Smith' and 'Ohinemuri' were thus obtained by the u se of cyanamide in an environment otherwise unsuitable for them, espec ially for the later cultivars on this list.